MaryJo, I wanted to mention for the sake of historical accuacy that there was no such thing as Czechoslovakia back in the time period you're talking about. Czechoslovakia did not come into existence until 1919! Czechslovakia existed as a country from 1919 to 1938, and again from 1945 to 1993.
Your relatives were from what was until 1918 the Austrian province of Bohemia (in German: Böhmen; capital: Prague). To the east of Bohemia is what was until 1918 the Austrian province of Moravia (in German: Mähren; capital: Brünn). Bohemia was about 50% German, 50% Czech. Moravia was about 70% Czech, 30% German.
Following World War I and the break-up of the Austro-Hungarian Empire by the Allies, Austria had to cede Bohemia and Moravia to the newly created Czechoslovakia, despite the large German population in both provinces. (Hungary had to give up Upper Hungary to form the Slovakia half of the new country.) Czechoslovakia ceased to exist in 1993, when Slovakia became an independent country. Bohemia and Moravia are the two components of today's Czech Republic.
Despite promises to the contrary, the Czech authorities did not treat the 3 million Germans of Bohemia and Moravia, who became known as the "Sudeten Germans", very well. The Sudeten Germans were made to feel like second-class citizens in their own country (as were the Slovaks, for that matter). The final result was the Munich Agreement of 1938, by which Czechoslovakia had to cede the German-populated "Sudetenland" to Germany.
Following World War II, the Allies resurrected Czechoslovakia. The 3 million Sudeten Germans were thereupon expelled from their homes by the Czech authorities.
I will refer you to a simple map of the pre-1919 Austro-Hungarian Empire, so that you can see how Bohemia fit into pre-1919 Austria:http://users.erols.com/mwhite28/austhung.htm